A typical form of a balancing machine for balancing a rotary member or rotor may comprise a mounting assembly for rotatably supporting the rotary member to be balanced, the mounting assembly being formed, for example, by two spaced-apart mounting stands on which respective ends of the rotary member are carried. A mounting stand of that kind comprises a stationary mounting block or pedestal arrangement which is fixed in a stationary position to a machine bed during an unbalancing measuring operation. As indicated above, a horizontal balancing machine has two such mounting stands, with the spacing therebetween being adjustable, depending on the size of the rotary member to be balanced. For that purpose the two mounting stands can be displaced on the machine bed in the axial direction of the rotary member, and are then fixed to the machine bed in order to carry out the unbalance measuring operation. A mounting means for the rotary member to be balanced is supported on each mounting block or pedestal arrangement of each mounting stand, by way of a support assembly consisting of mutually parallel springs. By virtue of its spring suspension, the mounting means for the rotary member forms an assembly which is capable of oscillating in a mounting plane in a measuring direction, with one degree of freedom. Operatively disposed between the stationary mounting block or pedestal arrangement and the oscillatable mounting means is a measurement value pick-up means which measures a force or a travel movement in response to oscillatory movement of the mounting means produced by an out-of-balance rotary member. Thus the mounting means reacts to an out-of-balance rotary member in accordance with its specific, frequency-dependent oscillation amplitudes and its phase, with a precisely defined oscillation vector which is detected by the pick-up means and which is suitably converted into a corresponding electrical measurement signal.
In order to ensure that variations with respect to the mounting stand, in particular the oscillatable system thereof, due to aging phenomena or due to operational factors, which occur in the course of time, do not falsify the measurement values produced by the assembly, adjustment is made to the balancing machine mounting assembly and in particular the oscillatable system of each of the two mounting stands, at certain intervals of time. The adjustment operation is carried out by using an unbalance-free adjusting rotor which is fitted into position in the balancing machine mounting assembly and which is used to carry out adjustment measuring runs, that is to say measuring runs which are required solely for the purposes of suitably adjusting and setting the machine. It will be appreciated that the requirement for adjusting the machine from time to time means that it is necessary to interrupt normal balancing operations, during which rotary members to be balanced are continuously fitted into the balancing machine mounting assembly and subjected to a measurement and balancing procedure therein. Furthermore, it is also necessary to keep an additional adjustment rotor in a condition of readiness for use when a machine adjustment operation is to be carried out. Also, the fitting and removing the adjustment rotor, for carrying out the adjustment operation, involve a considerable amount of time and work.